I just installed MacTeX 2010 yesterday, so I'm running TeXLive 2010. I need to upgrade my installation of PGF to 2.0 from 1.18, which is what comes standard with the MacTeX distribution. Could someone walk me through all the steps to do this, on a mac running 10.6, assuming I'm illiterate when it comes to installing TeX stuff?

I'd like to do the update not in my personal library (although if you can tell me how to make that work that would be great too) but in the main computer library, so the update will be available across users.

I tried following the instructions in the PGF manual, which said to put various files in various places:

To update your installation from a previous version, all you need to do is to replace everything in the directory texmf/tex/generic/pgf with the files of the new version (or in all the directories where pgf was installed, if you chose a tds-compliant installation).

but when I did that it didn't work. Possibly because I didn't "run texhash", whatever that is and however you do that.

To run texhash, open up a terminal, type in sudo texhash, and give your password when asked.
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Konrad SwanepoelOct 19 '10 at 21:29

I believe PGF 2.0 became standard issue in TeX Live 2008, so anything from MacTeX 2008 or later should have it. It is likely you have a copy installed in a texmf tree that supersedes the MacTeX distribution
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SharpieOct 20 '10 at 0:05

With fingers crossed, you shouldn't ever have to replace any files inside the main TeX distribution itself; TeX Live is good at updating itself these days and most packages are kept up-to-date on CTAN.